This invention relates to communication unit frequency (RF) communication systems, including but not limited to transmission of messages in RF communication systems.
The basic operation and structure of a land mobile communication unit system is well known. Land mobile communication unit systems typically comprise one or more communication units (e.g., vehicle-mounted or portable communication units in a land mobile system and communication unit/telephones in a cellular system) and one or more repeaters that transceive information via the RF communication resources. These communication resources may be narrow band frequency modulated channels, time division multiplex slots, frequency pairs, and so forth. Land mobile communication unit systems may be organized as trunked communication systems, where a plurality of communication resources is allocated amongst a group of users by assigning the repeaters on a communication-by-communication basis within an RF coverage area.
Large communication systems comprising a large number of communication units are known to exist. At times, when a site failure occurs in such a system, the communication units that are presently registered at a failed site will want to affiliate or register with an adjacent site in order to avoid being isolated from their group communications. At times, however, it is possible that a very large number of communication units will try to re-register at an adjacent site in a very short time frame, causing the control channel on which registration takes place to become flooded with requests and the site may subsequently become incapable of processing any requests, including normal communication requests.
At other times, there may be a need for a large number of communication units to transmit messages on a single channel in a short period of time. In a broadcast data system, a single transmission may target numerous receiving communication units, sometimes thousands of units. Because each of the units must send either an ACK (acknowledgment) or a NACK (negative acknowledgment) for each data frame, the return channel becomes inundated with thousands of messages, consuming valuable time on the communication channel. If use of the return channel is not coordinated, many of these messages are likely to coincide at least partially, resulting in corrupted ACKs and NACKs, rendering the transmitter unable to distinguish which messages were received successfully and which ones were not. One method for returning ACKs and NACKs via a return channel in a coordinated manner is to designate a particular time interval for each unit to transmit an ACK/NACK. When there are numerous communication units, such a system is wasteful of the communication channel, and messages will take a very long time to be transmitted.
Accordingly, there is a need for a method of coordinating transmission of a large number of messages on a single channel in an orderly fashion, such that all messages are received without taking an extraordinary amount of time or flooding the channel to such degree that the communication site becomes unusable.